Monostable blocking oscillator



April 28, 1964 J. MORWALD 3,131,315

MONOSTABLE BLOCKING OSCILLATOR Filed June 28, 1961 INVENTOP JOSEF MOERWALD United States Patent 3,131,315 MONOSTABLE BLOCKING OSCILLATOR Josef Miirwaid, Dachau, near Munich, Germany, assignor to Kienzle Apparate G.m.h.l-i., Viliingen, Black Forest,

Germany Filed lune 28, 1961, Ser. No. 120,3?5 Claims priority, application Germany July 16, 1960 4 Claims. ((31. 30788.5)

The present invention concerns monostable or triggered blocking oscillator arrangements, and more particularly such oscillator arrangements having a transistor as the operative element.

Such blocking oscillator arrangements are well-known and are widely used in electronics for the purpose of producing impulses in a predetermined manner. The transistor constitutes actually a switching element which cooperates with inductive feedback means. The latter usually comprise at least one primary inductance coil and at least one secondary inductance coil magnetically coupled with each other by being arranged on a common core. When the switching device, eg the transistor is rendered conductive a current is caused to flow through the primary inductance coil so as to reverse the previous magnetization of the core, and simultaneously an output pulse is produced which is the purpose of using this oscillator arrangement, and this output pulse can be used for various purposes in circuits or devices supplied therewith. For rendering the switching element, e.g. the transistor, conductive a control or trigger pulse is applied thereto, and at least during the period or duration of this control pulse current is supplied from a source of energy to the above-mentioned primary inductance coil. However, during the period of magnetization reversal of the core the switching element e.g. the transistor is additionally kept in conductive condition by means of a feedback arrangement which comprises, in addition to the abovementioned core and the primary inductance coil thereon, a secondary coil on the same core, a feedback current being induced in the secondary coil until the core is ma netized to saturation by the current through the primary coil. As soon as full saturation is reached the feedback circuit is deenergized and consequently the switching element, e.g. the transistor, ceases to be conductive and cuts off.

Before a blocking oscillator of the above-described type is capable of producing a further output pulse, it is necessary that the core of the inductive feedback arrangement returns, or is returned, to its previous condition of magnetization. Cores of the so-called soft type i.e. cores made of a material having a non-rectangular hysteresis characteristic return automatically to their normal or original remanent magnetic condition as soon as the current through the primary coil is switched off. In those cases where cores of a material having a rectangular hysteresis characteristic are used, it is necessary to provide a separate coil on the core which coil is usually supplied with a constant current so that the core is returned to its original condition when the reversing current through the primary coil is discontinued.

For well-known reasons, the return of the core from its reversed magnetization to its original magnetization or condition causes inductively in the coils opposite directed currents. For the purpose of this description these induced currents will be called cut-oif currents. The peak of such a cut-off current is the higher, the more rapidly the core returns to its original magnetic condition.

Previously, blocking oscillator arrangements of the general type described above have been equipped with electron tubes as the switching or active element. Under these conditions no great attention had to be given to the 3,131,315 Patented Apr. 28, 1964 magnitude of the above-mentioned peaks of the cut-off currents because electron tubes are comparatively insensitive against short-time voltage peaks appearing at the control grid.

However, it has been found that these voltage or current peaks constitute a serious danger if a transistor is used as the active element or switching element of a blocking oscillator because transistors are very sensitive to excessive voltages applied thereto. Obviously the danger of damage to a transistor in such an arrangement is particularly great if the core of the inductive feedback arrangement is desired to return to its original condition very rapidly which is necessary if high frequency pulse series are to be produced.

It is therefore a main object of this invention to provide for a monostable blocking oscillator arrangement of the transistor type which is so constructed that at least the base of the transistor is protected against excessive voltages derived from the feedback action.

It is a further object of this invention to provide for a blocking oscillator arrangement of the type set forth in which both the base and the collector of the transistor are protected against the danger of being damaged by excessive voltages derived from the feedback action.

It is a further object of this invention to provide an arrangement as mentioned above in which a drift-transistor can be used as the active or switching element.

It is still a further object of this invention to provide for an oscillator arrangement as mentioned above in which, even at an extremely high ratio between pulse duration and pulse interval dangerous voltage peaks cannot appear at the electrodes of the transistor. With above objects in view, the invention provides in a monostable blocking oscillator having a transistor and inductive feedback means including a primary and a secondary inductance coil, magnetically coupled with each other, in combination, a parallel combination of a resistance means and a diode connected in series with one end of said second inductmce coil, said diode being poled to shunt said resistance means except for current flow during appearance of an inductive voltage peak upon cut-off of the transistor; and a second diode connected between the base of the transistor and one terminal of the source of voltage operating the transistor whereby the base of the transistor is protected against excessive voltage derived from the feedback action.

In a modified form of the invention the arrangement further comprises an auxiliary circuit arrangement connected in parallel with the primary inductance coil and comprising a second diode in series with a second parallel combination constituting an integrating device and including a capacitor means in parallel with a second resistance means, so that also the collector of the transistor is protected against excessive voltage derived from the feedback action.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is a schematic circuit diagram illustrating a blocking oscillator arrangement according to the invention in which the base of the transistor thereof is protected against excessive voltage; and

FIG. 2 is a similar schematic circuit diagram illustrating a modified and improved embodiment of the invention in which both the base and the collector of the transistor in the arrangement are protected against excessive voltages.

Referring now to FIG. 1, the diagram illustraies first of all certain more or less conventional elements of a monostable blocking oscillator arrangement, namely a switching or control transistor T connected with a control or trigger pulse input E across a capacitor C1. Upon the application of a negative trigger pulse E as shown diagrammatically near the terminal E, to the base of the transistor T an output pulse A is delivered from the emitler electrode of the transistor T at the output terminal A. The arrangement is connected between points of diiferent potentials as indicated in the drawing. The collec or electrode of the transistor T is connected in series with a primary inductance coil K mounted on a magnetic core K which is to be assumed to have a non-rectangular hysteresis characteristic. The core K carries a secondary inductance coil K one end of which is connected with the base of the transistor T, while its other end is connected, as shown, in series with a parallel combination of a resistor R and a diode D The last mentioned elements together with the conventional resistor R constitute the feedback circuit of the device. A second diode D is connected between a source of positive potential and a junction point e located between the base of the transistor and the input terminal E. Under the conditions described above it is of importance that the diodes D and D are poled as indicated in the drawing. It is further to be noted that the coils K and K are wound in directions opposite to each other.

In operation, the above mentioned trigger pulse E is applied to the input terminal E and arrives at the base of the transistor T so as to render the latter conductive. Now a current can flow from the collector through the primary coil K so as to magnetize the core K different from its previous state of magnetization or opposite to its previous magnetization. Since usually the duration of the trigger pulse E is shorter than the time required for magnetizing the core K to full saturation, the above described feedback circuit serves to extend the period of conductivity of the transistor T. During the change of magnetization of the core K through the current flowing through the coil K the flow of a current is induced in the secondary coil K This feedback current flows via diode D which shunts the resistor R to the base of the transistor and keeps the latter in conductive condition until the core K is magnetized to full saturation. As soon as the core K is magnetized to full saturation the flow of current through the secondary coil K ceases. Thereupon the core K being of the above described material returns to its previous state of remanent magnetization. However, during this return to the previous state of magnetization, currents of opposite directions are induced both in the primary coil K and in the secondary coil K This induced current from the coil K reaches the collector of the transistor T. The thus induced current in the coil K tends to flow to the base of the transistor T. However, according to the invention the intensity of this current which cannot pass the diode D is reduced to a harmless amount by the arrangement of the resistor R in the feedback circuit. The diagram J is intended to show that a considerable negative voltage peak would exist in the feedback line were it not suppressed by the existence of the resistor R However, the existence of the resistor R would seriously limit the magnitude of the active feedback current which, as explained above, is desired to be applied to the base of the transistor T in order to produce the desired duration of its conductivity. Therefore the diode D is connected in parallel with the resistor R and is poled in such a manner that the resistor R is completely shunted during the active fiowof feedback current, but is entirely effective when the negative voltage peak appears after the saturation of the core K in the above described series of events. In addition, the diode D is provided between the junction point e and thus between the base of the transistor T and the positive voltage supply, this particular arrangement assisting in protecting the base of the transistor T because voltage peaks appearing upon cut-off of the transistor T are drained away toward the positive terminal of the voltage supply.

It is to be noted that for obvious reasons the resistivity of the diodes D and D also play their part in the advantageous operation of the device as shown.

The arrangement as described not only furnishes excellent protection of the base of the transistor by limiting the maximum blocking potential at the base, but also en sures a highly satisfactory ratio between pulse duration and pulse interval so that the arrangement can be used for high frequency pulse series. It is to be noted that other known blocking oscillator arrangements which comprise devices for protecting the switching element sulfer from the great disadvantage that the ratio between pulse duration and pulse interval is highly unsatisfactory.

May it be assumed that the voltage peak appearing upon cut-off in the feedback circuit (see diagram J is U and that the potential at the diode D is U the following equation applies:

It can be seen that the ratio between U and U depends entirely on the chosen dimensions of the resistors R and R and on the forward resistance of the diode D The pulse diagram I in FIG. 1 illustrates how the undesirable voltage peak formations according to the pulse diagram J (applying to the line portion between the coil K and the parallel combination R and D are almost entirely eliminated at the junction point 2.

While the above described arrangement according to FIG. 1 very satisfactorily eliminates any danger of harming the base of the transistor through voltage peaks derived from the feedback action, the collector of the transistor T is not yet protected thereby against similar voltage peaks.

Therefore the arrangement according to FIG. 2 is provided, according to the invention, with additional means for protecting also the collector of the transistor T. Generally the circuit of FIG. 2 is the same as that of FIG. 1. However, in this embodiment an integrating device or circuit, composed of a parallel combination of a resistor R and a capacitor C is connected in parallel with the primary inductance coil K This auxiliary circuit further comprises a third diode D as shown in FIG. 2. By this arrangement a voltage peak which otherwise would appear at the collector of the transistor T is limited by the diode D In operation, the negative peak voltage appearing across the coil K upon the return of the core K from its first magnetized state to its original remanent state reaches via the diode D the capacitor C and is integrated by the resistance opposed by the diode D Consequently a fiow of current from the coil K into the capacitor C is only possible during an extremely brief moment when the core K returns from its first magnetized state to its normal state. Consequently, when the capacitor C is charged, only the discharge resistor R will operate for attenuating the coil K However it is easy to give the resistor R such a dimension that it will practically remain without eifect. The actual purpose of the resistor R is to discharge the capacitor C so as to make it ready for the next cycle of operations. If the capacitor C and the resistance offered by the diode D are properly chosen, which oifers no difficulty to those skilled in the art, an attenuation of the core K takes place only during the rise time of the cut-off impulse. Consequently the core K is Without any load after this event. Consequently the ratio between pulse duration and pulse interval as well as the time required for the core K to return from magnetized state to its normal state are practically not affected thereby. This is the essential advantage obtained Then by the insertion of the additional circuit elements C and R As will be readily understood from inspection of FIG. 2, in the arrangement illustrated thereby only such voltages will appear at the collector of the transistor T as illustrated by the pulse diagram 1 In all other parts of the circuit illustrated in FIG. 2 the conditions remain exactly he same as those which are illustrated in and by FIG. 1 and described with reference thereto.

Summing up, it is to be stated that by the arrangement according to the invention the transistor T is most satisfactorily protected against harmful voltage peaks without however adversely affecting the desirable ratio between pulse duration and pulse intervals which are necessary if a blocking oscillator is intended to be used for high frequency pulse sequences. In addition it will be understood that the advantages of the above-described mrangements make it also possible to utilize as switching or control transistors so-called drift type transistors as described e.g. in Proceedings of the IRE, 1959, p. 973; 1960, pp. 3880-3831; 1961, pp. 1054, 1321 and 2188, which have the most desirable characteristic of being capable of extremely high switching speeds, but which are extremely sensitive to excessive voltages applied thereto.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of a monostable blocking oscillator differing from the types described above.

While the invention has been illustrated and described as embodied in a monostable blocking oscillator having a transistor and inductive feedback means, it is not intended to be limited to the details shown, since various modifications and structurm changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications Without omitting features that, from the standpoint of prior art, fairly constiute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a monostable blocking oscillator having a transistor having a base and an emitter-collector circuit, in combination, inductive feedback means including a magnetizable core, a primary and a secondary inductance coil mounted on said core and magnetically coupled thereby with each other, said primary inductance coil being connected across the emitter-collector circuit of the transistor in circuit with a source of voltage, said secondary inductance coil being connected in circuit with a source of reference voltage between the base of the transistor and one terminal of said source of reference voltage to constitute a feedback circuit, said feedback circuit comprising in series with said second inductance coil, a parallel combination of a resistance means and a diode, said diode being poled to shunt said resistance means except for current flow during appearance of an inductive voltage peak upon cut-off of the transistor; and a second diode connected between the base of the transistor and one terminal of said source of reference voltage whereby the base of the transistor is protected against excessive voltage derived from the feedback action.

2. In a monostable blocking oscillator having a transistor having a base and an emitter-collector circuit, in combination, inductive feedback means including a magnetizable core, a primary and a secondary inductance coil mounted on said core and magnetically coupled thereby with each other, said primary inductance coil being connected across the emitter-collector circuit of the transistor in circuit with a source of voltage, said secondary inductance coil being connected in circuit with a source of reference voltage between the base of the transistor and one terminal of said source of reference voltage to constitute a feedback circuit, said feedback circuit comprising in series with said second inductance coil, a parallel combination of a resistance means and a diode, said diode being poled to shunt said resistance means except for current flow during appearance of an inductive voltage peak upon cut-off of the transistor; an auxiliary circuit arrangement connected in parallel with said primary inductance coil and comprising a third diode in series with a second parallel combination constituting an integrating device and including a capacitor means in parallel with a second resistance means; and a second diode connected between the base of the transistor and one terminal of said source of reference voltage whereby the base and the collector of the transistor are protected against excessive voltage derived from the feedback action.

3. An arrangement as claimed in claim 1, wherein the transistor is a drift-transistor.

4. An arrangement as claimed in claim 2, wherein the transistor is a drift-transistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,599,964 Woodbury June 10, 1952 2,950,398 Johnson Aug. 23, 1960 3,005,157 Rees Oct. 17, 1961 

1. IN A MONOSTABLE BLOCKING OSCILLATOR HAVING A TRANSISTOR HAVING A BASE AND AN EMITTER-COLLECTOR CIRCUIT, IN COMBINATION, INDUCTIVE FEEDBACK MEANS INCLUDING A MAGNETIZABLE CORE, A PRIMARY AND A SECONDARY INDUCTANCE COIL MOUNTED ON SAID CORE AND MAGNETICALLY COUPLED THEREBY WITH EACH OTHER, SAID PRIMARY INDUCTANCE COIL BEING CONNECTED ACROSS THE EMITTER-COLLECTOR CIRCUIT OF THE TRANSISTOR IN CIRCUIT WITH A SOURCE OF VOLTAGE, SAID SECONDARY INDUCTANCE COIL BEING CONNECTED IN CIRCUIT WITH A SOURCE OF REFERENCE VOLTAGE BETWEEN THE BASE OF THE TRANSISTOR AND ONE TERMINAL OF SAID SOURCE OF REFERENCE VOLTAGE TO CONSTITUTE A FEEDBACK CIRCUIT, SAID FEEDBACK CIRCUIT COMPRISING IN SERIES WITH SAID SECOND INDUCTANCE COIL, A 